Modern Physics Letters A

We review some properties of a class of cosmological models which incorporate space and time variations of α in the light of recent observations.

We describe the current status of the High Resolution Fly's Eye detector. Recent results indicate that the UHE cosmic ray spectrum exhibits significant structure near 10¹⁹ eV. A few events are seen beyond 10²⁰ eV in contradiction to the AGASA ground array claim of no cut-off. The composition of the cosmic rays is found to change from a predominantly heavy to a predominantly light mixture between and 10¹⁷ and 10¹⁸ eV. No evidence for anisotropy, on either small scales or large scales is found, in contradiction to AGASA. Systematic errors and absolute energy scale issues are now being carefully considered to see how to partially resolve this discrepancy. A new experiment(FLASH) at the Stanford Linear Accelerator Center (SLAC) to measure the Nitrogen fluorescence efficiency more precisely is described.

We discuss (and debunk) ten common myths about cosmological perturbations in inflationary and ekpyrotic/cyclic models and their implications for future observations.

I discuss various thoughts, old and new, about the cosmological constant (or dark energy) paradox. In particular, I suggest the possibility that the cosmological "constant" may decay as , where τ is the age of the universe.

The Array for Microwave Background Anisotropy is a 7-element interferometer to be sited on Mauna Loa, Hawaii. The seven 1.2m telescopes are mounted on a 6-meter platform, and operates at 3mm wavelength. At the time of this meeting, the telescope is under construction at the Vertex factory in Germany. It is due to be delivered in the middle of 2004. A 2-element prototype instrument has already been deployed to Mauna Loa where initial tests are underway.

The PrimevAl Structure Telescope (PAST), will be used to locate and study the era the of the first luminous objects, the epoch of reionization. The first stars ionized the gas around them producing a pattern of ionization that reflects the large scale density structure present at the time. The PAST array will be used to sense and study this ionization, by mapping the brightness of 21 cm neutral Hydrogen Cosmic Background (HCB) at redshift from 6 to 25. The HCB disappears on ionization, allowing the study of large scale structure and of star formation at this very early epoch.

The VSA is an aperture synthesis array dedicated to measuring anisotropies in the Cosmic Microwave Background (CMB). It has observed in two configurations to measure the CMB power spectrum from ℓ=150–1600, detecting the first three acoustic peaks at good signal-to-noise. We now plan to enhance the telescope to allow observation at higher ℓ. This will allow measurement of the fourth and subsequent peaks and will allow us to break degeneracies that exist at present between cosmological parameters. In addition we will investigate the excess power detected by CBI at ℓ > 2000 and will conduct high-sensitivity searches for topological defects.

The role of cosmic defects in cosmology is entering its new phase—as a test for several fundamental physics, including unification theories and inflation. We discuss how to use the Cosmic Microwave Background (CMB) to detect cosmic strings, a type of cosmic defects, and how to use this result to constrain the underlying physics. In particular, we use the simulations for the Array for Microwave Background Anisotropy (AMiBA) to demonstrate the power of this approach. The required resolution and sensitivity in such a method are discussed, and so is the possible scientific impact.

We present simulations of interferometric Sunyaev-Zel'dovich effect (SZE) and optical weak lenisng observations for the forthcoming AMiBA experiment, aiming at searching for high-redshift clusters of galaxies. On the basis of simulated sky maps, we have derived theoretical halo number counts and redshift distributions of selected halo samples for an AMiBA SZE survey and a weak lensing follow-up survey. By utilizing the conditional number counts of weak lensing halos with the faint SZE detection, we show that a combined SZE and weak lensing survey can gain an additional fainter halo sample at a given false positive rate, which cannot be obtained from either survey alone.

Due to the finite-size beam, interferometry observations of the CMB polarization tend to measure a mixture of E and B modes arising from uw-space smearing. We propose an interferometry observation strategy that can disentangle the polarization E and B modes in a clean manner. This strategy employs a similar principle as that of the single-dish observation proposed earlier, but requiring additional linear combinations of signals measured from different baselines. In this work, we consider a hexagonally packed interferometry array as an example to demonstrate the ultility and efficiency of the proposed method. The measurement from a unit cell of equilateral triangular baselines in interferometry measurement is found to be comparable to that from a single dish in single-dish measurements.

We report an instantaneous heating scheme at z=2 that can produce bound objects obeying the observed mass-temperature and luminosity-temperature relations. Such heating reduces the Sunyaev–Zeldovich (SZ) flux by a factor 3–2 on scale of 4–6 arcminutes. It exacerbates the need for the matter-fluctuation normalization to σ₈ to assume an exceedingly high value (~1.2), if the several-arcminute excess anisotropy detected by the CBI experiment is entirely caused by the SZ effect of inter-galactic hot gas. By contrast, we find that the several-arcminute excess detected by ACBAR can be consistent with the preheated SZ signals of σ₈=1.

I review the recent 5D self-tuning solutions of the cosmological constant problem, and try to unify two cosmological constant problems within the framework of the self-tuning solutions. One problem, the large cosmological constant needed for inflation, is interpreted by starting with the parameters allowing only the dS vacuum, and the vanishing cosmological constant at a true vacuum is realized by changing parameters by exit from inflation at the brane such that the self-tuning solution is allowed.

While there exist various candidates, the nature of dark matter remains unresolved. Recently it was argued that the generalized uncertainty principle (GUP) may prevent a black hole from evaporating completely, and as a result there should exist a Planck-size black hole remnant (BHR) at the end of its evaporation. If a sufficient amount of small black holes can be produced in the early universe, then the resultant BHRs can be an interesting candidate for DM. We demonstrate that this is indeed the case for the hybrid inflation model. By assuming BHR as DM, our notion imposes a constraint on the hybrid inflation potential. We show that such a constraint is not so fine-tuned. Possible observational signatures are briefly discussed.

We discuss possible roles in the Early Universe of the electroweak (EW) phase transition, which endows masses to the various particles, and the QCD phase transition, which gives rise to quark confinement and chiral symmetry breaking. Both phase transitions are well-established phenomena in the standard model of particle physics. Presumably, the EW phase transition would have taken place in the early universe at around 10^-11sec, or at the temperature of about 300 GeV while QCD phase transition occurred between 10^-5sec and 10^-4sec, or at about 150 MeV. In this article, I wish to model the EW or QCD phase transition in the early universe as driven by a complex scalar field with spontaneous symmetry breaking such that the continuous degeneracy of the true ground states can be well represented. Specific interest has been directed to nucleation of domains, production of domain walls, and subsequent re-organization of domain walls resulting in "domain-wall nuggets". It is suggested that the domain-wall nuggets contribute to dark matter in the present Universe.

Diverse cosmological observations indicate the existence of dark energy, comprising ~ 70% of the total cosmic energy density and driving the accelerated cosmic expansion. Possible explanations for the dark energy include a cosmological constant and quintessence — a time-varying, inhomogeneous field with negative pressure. In this article we summarize how the dark energy imprints features on the cosmic microwave background. Observation of these features could be useful in discriminating amongst various theories, and could reveal clues as to the nature of the dark energy.

We discuss several possibilities of probing string theory through cosmology, e.g., the imprints of short distance physics on CMB anisotropies, the signatures of brane inflationary models, and the cosmological constraints on D-matter.

We study the concentration parameters, their mass dependence and redshift evolution, of dark-matter halos in different dark-energy cosmologies with constant and time-variable equation of state, and compare them with "standard" ΛCDM and OCDM models. The dependence of averaged halo concentrations on mass and redshift permits a simple fit of the form (1+z)c=c₀(M/M₀)^α, with α≈-0.1 throughout. We find that the cluster concentration depends on the dark energy equation of state at the cluster formation redshift z_coll through the linear growth factor D₊(z_coll). As a simple correction accounting for dark-energy cosmologies, we propose scaling c₀ from ΛCDM with the ratio of linear growth factors, c₀→c₀D₊(z_coll)/D₊,ΛCDM(z_coll).

We perform a set of ray-tracing simulations, using numerical cluster models, aiming at evaluating how the galaxy cluster efficiency for producing strong lensing events changes in different cosmological models with dark energy. The sample of investigated clusters for which we present our results here is composed by 7 dark matter halos. Each of them was simulated in 8 different cosmological models with constant and time-variable equation of state of dark energy. For all the clusters in the sample, we have measured the lensing cross sections for producing giant arcs, i.e. arcs having a minimum length-to-width ratio. We find that the lensing cross section for giant arcs is sensitive to the equation of state of quintessence. Indeed, the optical depth, which can be translated into a number of arcs by multiplying by the correct density of source galaxy on the sky, spans more than one order of magnitude among different cosmological models.

We study the time variation of the fine structure constant driven by quintessential dark energy which is coupled to electromagnetism. By employing phenomenological quintessential models which provide the scalar field with maximal dynamics and satisfy the constraints from SNIa observations and the WMAP, we show that the fifth force experiments restrict the variation of the value of α at the decoupling epoch with respect to the present-day value from being less than about 0.1%.

This is a short overview of spatially flat (or open) four-dimensional accelerating cosmologies for some simple exponential potentials obtained by string or M theory compactification on some non-trivial curved spaces, which may lead to some striking results, e.g., the observed cosmic acceleration and the scale of the dark energy from first principles.

The IceCube Neutrino Telescope, a huge Neutrino Telescope with 1 cubic km instrumented volume, starts construction in 2004. The project status and the expected sensitivity and performance for detecting high energy cosmic neutrinos are reported. Preliminary results based on AMANDA experience without taking into account IceCube's new digital technology indicate a sensitivity to a diffuse muon neutrino energy flux of 10^-8 GeV/cm² sr sec. Proposed models for GRB emission should be observable in less than one year. The capability of EHE neutrino detection is also briefly mentioned.

The Ashra detector consists of 3 observational stations installed on the grid of 30-40km distance on the mountains on the Hawaii Big Island, which ensures a large target mass for neutrinos and a large effective aperture for UHECR. An observational station is composed of 12 wide-angle high-precision telescopes, which can completely cover allsky view. In realizing the telescope design, we newly apply the following techniques matured in the other fields: 1) Baker-Nunn optics optimized to keep better than 1 arcmin. resolution in 50° field of view, 2) Electro-static lens image-intensifier tube (IIT) with the resolution matched with that of the above optics, 3) Gated IIT with a fast image shutter, and 4) CMOS image sensor which reads triggered images out of the above IIT.

These novel techniques allow us an excellent opportunity for simultaneous observation of air fluorescence and Cerenkov lights with 1 arcmin. resolution in entirely all sky. This will open an interesting field, "Observational Particle Astronomy" by continuously observing TeV gamma-rays, VHE-neutrinos, Knee-CR, and EHECR with the energies from TeV to ZeV in all sky.

The NuTel collaboration is building a wide field-of-view Čerenkov telescope to be installed on a mountain site for observing near horizontal air showers emerging from another mountain. Cosmic tau neutrinos is the primary source of such showers. This technique will be realized for the first time in the ν_τ energy range of 2 PeV to 1000 PeV. The telescope has enough sensitivity to observe cosmic neutrinos from sources like Active Galactic Nuclei and Galactic Center assuming fluxes from current theoretical models.

In this talk, we elaborate the strategy for detecting the Earth-skimming tau neutrinos. We first show that there are non-negligible astrophysical tau neutrino fluxes due to neutrino flavor oscillations. We then illustrate the idea of detecting Earth-skimming tau neutrinos. In particular, we point out that the tau-lepton flux resulting from neutrino-nucleon scatterings inside the earth is controlled by the tau-lepton range. We demonstrate this observation by showing the tau-lepton flux induced by the GZK tau-neutrino flux. The question on the energy resolutions of tau neutrinos in this detection strategy is briefly discussed.

Regarding ultrahigh-energy cosmic rays (UHECRs) as a probe and extra dimensions as a possible ingredient of the fantastic ultrahigh- energy world, we discuss possible interplay between them. On the one hand small extra dimensions and KK bursts present a feasible way to the origin of UHECRs. On the other hand large extra dimensions may change various interactions between particles at ultrahigh energies and therefore impact on air showers created by UHECRs. Conversely, UHECR data may tell us secrets veiled in extra dimensions.

We focus on the arrival direction distributions of the ultra-high energy cosmic rays (UHECR) in search of their possible origins. Models which associate the origin of UHECR with decays of relic superheavy dark matter particles (SHDM) predict the anisotropy of UHECR flux toward the Galactic center. We use the existing SUGAR data, which cover the Galactic center, to look for such a signal and limit the fraction of UHECR produced by this mechanism.

We first give a review of solar neutrinos, followed by an analysis of atmospheric neutrinos. Finally, we discuss neutrinos in cosmology and ultra high energy neutrinos.

We discuss the implications of a new scalar field coupled to neutrinos.

It is shown how high energy neutrino beams from very distant sources can be utilized to yield information about properties of neutrinos such as lifetimes and the possible mass hierarchy.Furthermore, mixing elements such as U_e3 and the CPV phase in the neutrino mixing matrix can be determined in principle. Pseudo-Dirac mass differences as small as 10^-18eV² can be probed as well.

Neutrinos with energy greater than GeV are copiously produced in the p(A,p) interactions occurring in the earth atmosphere and in our galactic plane. A comparison of the tau and mu neutrino flux in the presence of neutrino oscillations from these two astrophysical sites is presented. It is pointed out that the galactic plane tau neutrino flux dominates over the downward going atmospheric tau neutrino flux at much lower energy value than that for the dominance of the mu neutrino flux from these two sites. Future prospects for possible observations of galactic tau neutrino flux are also briefly mentioned.

Bubble collisions in cosmological phase transitions are explored, taking the non-abelian character of the gauge fields into account. Both the QCD and electroweak phase transitions are considered. Numerical solutions of the field equations in several limits are presented.

Casimir vacuum energy is divergent. It needs to be regularized. The regularization introduces a renormalization scale which may lead to a scale dependent cosmological constant. We show that the requirement of physical cosmological constant is renormalization scale independent provides important constraints on possible particle contents and their masses in particle physics models. In the Standard Model of strong and electroweak interactions, besides the Casimir vacuum energy there is also vacuum energy induced from spontaneous symmetry breaking. The requirement that the total vacuum energy to be scale independent dictates the Higgs mass to be where the summation is over fermions and N_i equals to 3 and 1 for quarks and leptons, respectively. The Higgs mass is predicted to be approximately 382 GeV.

We present cosmological perturbation theory based on generalized gravity theories including string correction terms as well as a tachyonic complication. The classical evolution as well as the quantum generation processes in these variety of gravity theories are presented in unified forms. These apply both to the scalar- and tensor-type perturbations.

This article reviews the research program and efforts for the TEXONO Collaboration on neutrino and astro-particle physics. The core program is on reactor-based low energy neutrino physics at the Kuo-Sheng (KS) Power Plant in Taiwan. The facilities of the laboratory is described. A limit on the neutrino magnetic moment of at 90% confidence level was derived from measurements with a high purity germanium detector. Other physics topics at KS, as well as the various R&D program, are discussed.

In this talk I review some general ideas of effective field theory and give examples of high precision calculations which have astrophysical applications. The examples are np→dγ for big-bang nucleosynthesis and νd inelastic scattering relevant for the solar neutrino detection processes employed by the Sudbury Neutrino Observatory.

The fields, created from quantum fluctuations during inflation era, are known to be in squeezed quantum states. And recent studies show that the Planck scale physics can have observable cosmological effects. We investigate here how the squeezed quantum states are influenced by the trans-Planckian cutoff which modifies the dispersion relation on subhorizon scales, and calculate the particle production at the end of the inflation.

We show that the idea that CDM are decaying superheavy particles which produce UHECR with energies beyond the GZK cutoff may simultaneously solve the problem of subgalactic structure formation in CCDM model. In particular, the Kuzmin-Rubakov's decaying superheavy CDM model may give an explanation to the smallness of the cosmological constant and a new thought to the CDM experimental search.

Entropy production by a dilaton decay is studied in the model where the dilaton acquires potential via gaugino condensation in the hidden gauge group. Its effect on the Affleck-Dine baryogenesis is investigated. It is shown that the baryon asymmetry produced by this mechanism with the higher-dimensional terms is diluted by the dilaton decay and can be regulated to the observed value.

Measurements of the electric dipole moment (EDM) of the neutron and the electron put the most stringent constraints on new sources of CP violation. CP violation is essential for generating the observed baryon asymmetry of the universe (BAU). Many models which propose large CP-odd mechanisms for BAU predict EDMs that exceed the limits of the most sensitive measurements. We are conducting a high sensitivity search for the electron EDM using a solid state system. It promises orders of magnitude improvement over atomic beam experiments solely from the available electron density. We present the experimental design and report on the current status.

A search of neutrino magnetic moment was carried out at the Kuo-Sheng Nuclear Power Station at a distance of 28 m from the 2.9 GW reactor core. With a high purity germanium detector of mass 1.06 kg surrounded by scintillating NaI(Tl) and CsI(Tl) crystals as anti-Compton detectors, a detection threshold of 5 keV and a background level of 1 kg^-1kev^-1day^-1 at 12-60 keV were achieved. Based on 4712 and 1250 hours of Reactor ON and OFF data, respectively, the limits on the neutrino magnetic moment of at 90(68)% confidence level were derived. Indirect bounds of the radiative lifetime of can be inferred. The present status and future plans are discussed.